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Summary Outline
Introduction
- The urinary system helps keep the body in homeo-
stasis by removing and restoring selected amounts of
solutes and water from the blood.^
- The system consists of two kidneys, two ureters, the
bladder, and the urethra.^
- The kidneys are the main filtering organs of the sys-
tem, producing the urine.^
- Urine consists of urea, excess water, excess ions, and
toxic wastes that may have been consumed with food.
Functions of The Urinary System
The kidneys perform six functions as they daily filter
the blood:
- Excretion. They are the major excretory organs of
the body, filtering large amounts of fluids from the
bloodstream, including nitrogenous wastes, drugs,
and toxins.^
- Maintain blood volume and concentration. They
regulate the proper balance of water and dissolved
salts by maintaining proper ion concentrations.^
- pH regulation. They control the proper hydrogen
ion concentration of the blood.^
- Blood pressure. They produce the enzyme renin,
which helps maintain blood pressure.^
- Erythrocyte concentration. They produce the pro-
tein hormone erythropoietin, which stimulates red
blood cell production.^
- Vitamin D production. They convert vitamin D to
its active form (calciferol).
The External Anatomy of The Kidneys
- The kidneys are located just above the waist between
the parietal peritoneum and the posterior wall of the
abdomen.^
- The hilum is a notch in the concave center of each
kidney through which a ureter leaves the kidney and
blood vessels, nerves, and lymph vessels enter and exit
the kidney.^
3.^ Three layers of tissue surround each kidney.^
4. The innermost layer is the renal capsule that acts as a
barrier against infection and trauma.^
- The second layer is the adipose capsule, a mass of
fatty tissue that protects the kidney from blows.^
- The outermost layer is the renal fascia that anchors
the kidney to the abdominal wall.
Chapter 18The Internal Anatomy of The Kidneys1.^ The outer area of a kidney is called the cortex.^
2.^ The inner area of a kidney is called the medulla.^
3. Within the medulla are striated, triangular struc-tures
called the renal pyramids whose bases face the cortex
and whose tips are called renal papillae that point to
the center of the kidney.^
4. The cortical material that extends between the pyra-
mids is called the renal columns.^
5. The cortex and renal pyramids make up the paren-
chyma of the kidney, which is composed of millions
of microscopic units called nephrons.^
6.^ The nephrons are the functional units of the kidneys.^
7. The tip of each renal pyramid is surrounded by a
funnel-shaped structure called a minor calyx, which
collects urine from the ducts of the pyramids.^
8. Minor calyces join to form a few major calyces. The
major calyces join to form the large collecting fun-
nel called the renal pelvis, which narrows to form the
ureter.
The Anatomy of The Nephrons- A nephron is a microscopic renal tubule and its vas-
cular component.^ - The nephron begins as a double-walled globe
known as Bowman’s glomerular capsule.^ - The innermost layer of the capsule is the visceral layer
made of podocytes. These epithelial podocytes
surround a capillary network called the glomerulus.^ - The outermost layer of the capsule is called the
parietal layer.^ - A renal corpuscle is made up of Bowman’s glomeru-
lar capsule and the enclosed capillary glomerulus.^ - The visceral layer of Bowman’s capsule and the capil-
lary network of the glomerulus form the endothelial-
capsular membrane, which filters water and solutes
from the blood and moves it into the renal tubule.^ - The first part of the renal tubule is called the proxi-
mal convoluted tubule, located in the cortex.^ - The following part is the descending limb of Henle,
which narrows as it dips into the medulla. The tu-
bule then bends into the U-shaped loop of Henle.^ - As the loop straightens, it increases in diameter and
ascends toward the cortex as the ascending limb of
Henle.^ - In the cortex, the renal tubule again becomes con-
voluted and is known as the distal convoluted tu-
bule, which ends by merging with a large, straight
collecting duct.